Novel IFT122 mutation associated with impaired ciliogenesis and cranioectodermal dysplasia

Abstract

Cranioectodermal dysplasia (CED) is a very rare autosomal recessive disorder characterized by a recognizable craniofacial profile in addition to ectodermal manifestations involving the skin, hair, and teeth. Four genes are known to be mutated in this disorder, all involved in the ciliary intraflagellar transport confirming that CED is a ciliopathy. In a multiplex consanguineous family with typical CED features in addition to intellectual disability and severe cutis laxa, we used autozygosity-guided candidate gene analysis to identify a novel homozygous mutation in IFT122, and demonstrated impaired ciliogenesis in patient fibroblasts. This report on IFT122 broadens the phenotype of CED and expands its allelic heterogeneity.

Keywords: Ciliopathy; craniosynostosis; intraflagellar transport.

Figure 1

The family reported in this study. (A) Pedigree of the family with the index case boxed in red. Facial and hand profiles for the two male patients are given in (B) and (C). Note the typical facial features (prominent forehead, depressed nasal bridge, anteverted nares, and everted lower lip) and typical hand features (brachdactyly, single interphalangeal crease for some fingers and clinodactyly). Please note the redundant palm skin in the lower panels, consistent with cutis laxa.

Figure 2

A missense mutation in IFT122 causes cranioectodermal dysplasia in the reported family. (A) Homozygosity Mapper reveals two regions of autozygosity which are shared by the three patients genomewide. The IFT122 locus is indicated with an arrow. (B) Sequence chromatogram of one control individual and one patient, with the site of mutation denoted by an asterisk. (C) Schematic of the IFT122 protein indicating the position of WD40 domains. The mutation reported here is located with a green arrow, while all previously published mutations are given below the schematic (red arrowheads). (D) Protein alignment data reveal that the affected amino acid residue is highly conserved across species, down to moss and trichoplax.

Figure 3

Primary cilia in patient cells exhibit reduced frequency and length as compared with control cells. Primary cilia from serum-starved primary control (A) and patient (B) fibroblasts, stained with anti-acetylated tubulin (green) and counterstained with 4',6-diamidino-2-phenylindole (blue). (C) Patient cells show significantly decreased ciliogenesis versus control cells (P < 0.0001, Fisher's exact test). All cells within a total of six fields, representing two independent experiments, were counted for each cell line. Error bars represent the standard error of the mean. (D) Patient cells show significantly decreased ciliary length versus control cells (P < 0.002, unpaired t-test). Error bars represent the standard error of the mean.